Casement or hinged window closures have become very common in recent years, largely supplanting double-hung or other sliding type closures for window openings, particularly in apartments but also in many private homes. In these windows a frame is fixedly mounted in the opening and a separate frame, carrying the glass window, is hingedly connected to the fixed frame.
In order to provide a device for opening and closing the hinged portion a crank-operated device is mounted on the fixed frame with a link passing through a relatively small opening in the fixed frame, the link comprising a flat bar pivotally connected at one end to the movable frame and at the other end to an arm of the device. The arm is normally formed on a sector gear, the teeth of which engage a worm gear, the sector and worm gears being rotatably disposed within a relatively flat housing mounted on the fixed frame.
A manually operated crank is provided on the housing and coupled to the worm gear so that rotation of the crank rotates the worm gear which, in turn, rotates the sector gear, moving the arm and link to open or close the window.
Window operators of this type have conventionally been produced using metallic materials, commonly zinc or similar alloys, for reasons of cost and strength, and because such alloys resist corrosion and other detrimental environmental effects. Production of these relatively simple devices is, however, rather expensive because of the need to machine the worm gear thread or tooth and the sector gear teeth. In addition it is very expensive to assemble the metal operators because of the multiple steps and machine operations necessary. In particular, the connection of the operating link to the sector gear arm requires deformation of a metal stud or fastener. The knob must be pinned or riveted to the worm shaft and the sector gear axle must be fastened to the housing by a rivet technique.
There has been a desire to produce window operators for this purpose, particularly as replacement devices but also for new construction using "plastic" materials, particularly polymeric materials because this would permit components such as the sector and worm gears to be molded rather than machined or forged, thereby greatly reducing the cost of manufacture. Broken parts could also be replaced in the field. However, problems of strength of the polymeric materials has prevented the successful manufacture thereof. In this context it will be recognized that the mechanical forces involved are rather large. As will be apparent from the more detailed discussion hereinafter, if the window tends to stick or in any way to resist motion, the worm and sector gear, being rather small components, are subjected to large forces which tend to destroy those components if they are simply made from the polymeric materials rather than metal, using substantially the same design criteria.
It is, of course, not feasible to change the basic design of window operators of this type and for this general purpose, particularly if they are to be used to replace worn-out operators of conventional design. Thus, the spacing of the openings to attach the operator housing to the fixed frame must be the same; the housing must fit in the same location, usually with very small clearance, adjacent the frame and sill; the arm and link must pass through the same opening in the frame and operate the window in essentially the same fashion; and the housing and crank should present substantially the same appearance as to shape for functional as well as customer acceptance reasons.